Capillary oxygenator



Feb. 21, 1961 R. A. DE WALL CAPILLARY OXYGENATOR Filed Dec. 24, 1958 I NVEN TOR. Fla-HARD A. DE Wm.

%M MM ATTORNEYJ United htates Patent 2,912,349 CAPILLARY' OXYGENATOR Filed Dec.- 24, 1958, Ser. No. 782,737 Y 9 Claims. or, 128-214) This invention relates to a liquid-gas or aliquid-liquid membrane exchange device and especially toa device for oxygenating blood in an extracorporeal circulation system for temporarily assuming'or assisting the functions of the heart and lungs in a human being or other animaL-or for use as anartificial kidney. For convenience, the-device of this invention will be described as it relates toa device for introducing oxygen into' blood and releasing carbon dioxide from blood outside of thebody of a human or other animal during cardiac surgery, although it will be understood that the same structure isuseful in other applications in the treatment of humans and other animals. When used as an oxygenating device which temporarily assumes the functions of the lungs,- the-device is used-with a standard blood pump which temporarily assumes'the function of the heart by circulating-the'blood through the :oxygenator.

The desirability and necessity of temporarily relieving the heart of its normal function of pumping blood during cardiac surgery have long been recognized, and the con cept of extracorporealcirculation is generally old in the art. Such a system is disclosed in United States Patent No; 2,854,002 issued to De Wall et al. on September 30; 1958. The oxygenator' of thepresent invention" utilizes the same pumping apparatus and receives and returns the blood insubstantially the same manner described in' tha't patent. Oxygenation, according'to the present invention, is accomplished, however, by passing the blood through a plurality of thin-walled capillary tubes capable of gas transmission while maintaining the capillary tubes surrounded by oxygen.

his the principal object of'this invention to provide-a simple capillary membrane liquid-gas or liquid -liquid ex change devicefor the treatmentand purification of body fluids.

It is another object of this invention to provide a relatively simple closedsystem capillary oxygeriatingfiand carbon dioxide releasing device for use in direct vision intracardiac surgery and similar applications;

Other objects of theinvention will become app'arent'as the description proceeds.

To the accomplishment-of the foregoing and related ends, this invention then comprises the'features herein after fully described-and particularly pointed out inthe claims, the following'description setting'forth in detail certain illustrative'embodiments of the invention, these being indicative, however, of but a-few of the various ways in which theprinciples of the inver'ition maybe employed.

The invention is illustrated by the drawings'in which the same numerals refer to corresponding parts andin which:

Figure-l is an eleva'tion' of one face of the capillary oxygenatof'according to this invention shown with the front surface partially broken away to reveal theinner construction;

FigureZ 'is' a vertical sectiontaken on the li 2-2 2,972,349 Paitented Feb. at,

ice

of Figure -1and"in the direction of the arrows revealing the inner construction of the oxygenator unit; and

Figure 3 is a-top plan view of theoxygenator unit.

Referring to'the-drawings, the oxygenator unit of this invention includes agenerally rectangular plastic box structure havingatop wall 11, a bottom-wall 1 2, and end walls 13 and 14. The wall components are preferably composed of a synthetic resinous plastic material" as pointedout with greater particularity hereinafter. The oxygenator'wall componentsare desirably composed of resilient and pliable plastic sheet material'of sufficient thicknessto impart substantial" rigidity to the-boxstruc ture. A relativelythinner film-cover sheet 15 is attached to the front edge portions of thetop, bottom, and end walls, and a similar film covering 16 is attached to-the back edges 'ofthe--top,-bottom,- and end walls.

A front Wall'n'iember'17is'fitted between the top and bottom walls and between the two end walls-"spaced inwardly from the front edgesthereof and'fromthedr'ont face'covering 15 to definea relatively thin shallow blood inlet chamberor reservoir 18; A similarback wall'r'nember19 is positioned between the top and-bottom walls and between the end walls spacedslightly inwardly from the rear edges thereof and from the -bac-k--face*covering 16 to provide a narrow shallow blood-discharge chamber or reservoir 20. v The exposed outer faces of-the front-arid back walls 17 and'1 9 are provided withhundreds-of s'rhall capillary openings 21. a The corresponding capillary openings in the front and 'rear walls are connectedby'ala'lural ity of thin-walled capillary tubes 22;

A blood inlet fllbf23 communicates "withtheblood inlet chamber 1 8. For convenience, the blood inlet 't'ube' extendsthrough the top-wallll and fron't'wall 17 'open inginto the chamber-18; A similarblood-discharge tube 24 extends through the back wall 1'9'andtop"wal1 11 communicating -with the-blood discharge dliamberZO. The space between the front; back, top,'bottom,'and'sid walls, largely occupiedby the capillary tubes 22; is" a-gas exchange chamber or-anoxygenating: chamber 251' An air or oxygen gas inlet 26 communicates directly with the oxygenating cha mber through the'top'wall adjacent the back wall 18 of the oxygenatingunit, and' acarbon dioxide gas discharge 2 7 communicates directlytwitli'the oxygenatingchamber adjacent the'fr'ontwall -17 of the oxygenator.

During heart surgery, venous blood froni apatie'ntis pumped to the blood inlet tube-23 and intothe blood inlet chamber or reservoir 18. At'the'same time, air'or oxygen-under pressure'is introduced into:tlieoXygenating chamber 25 through gas inlet 26. The pressure of the blood in the inlet reservoir forces the venous blood through the'many capillary tubes 22 and into the dis charge reservoir 20. From'this blooddischarge chant ber, the blood is forced through the blooddischa'rgetube 24 and pumped backto the pati'ent.- In the course ofthe passage through' the capillary'tube's, oxygenpenetrates the gas permeable walls of thetubes and 'displaces' tlie carbon dioxide in the blood. The carbon dioxide'es'cape's' in the same manner through the walls of the capillary tubes, and is discharged through gas' outlet tube 27 by the continuous flow ofgas maintained through the oxy enating chamber. Where greater oxygenatingcapacity'is required than'canbe furnished by one oxygenatin'g'unit, two or more oxygenating units may be connected in parallel. i l! The oxygenator unit, according to this invention; is preferably composed completely of a synthetic-resinous plastic material; The oxygenato'r'may becomposed entirely of a single resinous material or of a combination of compatiblematerials. The materials of which the capillary tubes -22 are formed must be-permeable to the transmission of both oxygenvand carbon'dioxida'as -vir tually all synthetic resinous materials are in thin layers. Exemplary materials include silicone rubber (Silastic), polyvinyl chloride, polyethylene, vinylidene chloride polymers, tetrafiuoroethylene polymers, trifiuorochloroethylene polymers, rubber hydrochloride, and the like. The plastic material should be pure, non-toxic, strong, capable of being sterilized, and preferably at least partially transparent. ture, the synthetic resinous material is desirably also heat sealable.

The capillary openings 21 and the capillary tubes 22 should have diameters in the range between about 1 to 50 mils and, preferably, from about to 20 mils. At the same time, the capillary tubes shouldhave a wall thickness between about 0.5 to 2 or 3 mils. These dimensions have necessarily been shown greatly exaggerated in the drawing. The capacity of any given oxygenator unit is dependent upon the area of capillary tube surface exposed to oxygen in the oxygenating chamber 25. As a typical example, an oxygenator is formed which is approximately six inches square with the front and baclcwalls 17 and 19 spaced approximately two inches apart. The average diameter of the capillary openings 21 is about mils, and the average wall thickness of each of the capillary tubes is about 2 mils. The outside diameter of each capillary tube is thus 0.014 inch, and the outside surface area of each tube is 0.088 inch. The oxygenator unit is formed with 32 rows of 32 capillary openings in each row, giviing a total of 1,024 capillary tubes. The total surface of capillary tubing exposed to oxygen within the oxygenating chamber is thus 90 inches.

In general, the oxygenator preferably is provided with between about 500 and 2,000 capillary openings, and the capillary tubes are desirably between about 1 and 4 inches long. Thus, assuming the average dimensions recited above, oxygenators can bemade providing from about 22 to about 360 square inches of gas exchange surface. Although greater capacity can be introduced by increasing the size of the oxygenator, increasing the number of capillary tubes, increasing the length of the capillary tubes, etc., it is more convenient to manufacture the oxygenating unit in standard sizes and gain increased capacity where needed by the use of two or more oxygenating units connected in parallel.

The oxygenator unit may be made, for example, by inserting preformed capillary tubes into preformed capillary openings formed in the front and back walls. It is preferred, however, to form the capillary tubes integral with the front and back walls. This is accomplished, for example, by means of a pair of parallel plates spaced apart by the desired distance between the outer faces of the front and back walls and interconnected by a plurality of pins extending between the plates and being separable from at least one of them. A typical arrangement, for example, is one plate having the desired number of pins projecting from one face and permanently attached, and a companion perforated plate adapted to receive the free ends of the pins in its perforations. Resin is then desirably cast on the inside faces of those plates so as to provide the front and back walls with substantial thickness capable of supporting the capillary tubes. The capillary tubes themselves are cast around the pins extending between the parallel plates by dipping the plates and pins into a suspension or solution of the resinous material. The resinous material is deposited on the surfaces of the pins and built up to form tubes of desired wall thickness. Care is exercised to prevent bridging of the plastic material between adjacent pins.

The composite structure comprising the front and rear walls and interconnecting capillary tubes are carefully stripped from the molding form pins to avoid rupturing any of the thin-walled capillary tubes. The blood inlet and discharge tubes are inserted through the top wall member, and the front and back wall members. The

For ease in assembly and manufacgas inlet and discharge tubes are inserted in the top wall and the bottom and side walls are all secured in place. In assembling the oxygenator unit, care is taken to seal all seams between adjacent elements to prevent escape of gas from the oxygenating chamber into either of the blood chambers. Depending upon the particular resins used, sealing may be accomplished by means of heat, solvents, or compatible resinous adhesive materials. Thereafter, the front and rear face covering films are sealed in place.

As an example of the described general method, a quantity of silicone rubber (Silastic 971*1, Dow-Corning) is first milled on rubber milling equipment and then diluted with about 7 percent by Weight of benzoyl peroxide plasticizer compounded with silicone rubber (Luperco ASF). A suspension of this material is pre' pared in xylene. A Teflon mold made up of a plurality of Teflon coated wire pins held between a pair of Teflon plates is dipped into the suspension and withdrawn. It is dipped and redipped until the desired thickness of rubber is deposited. The unit is given a preliminary cure by autoclaving at about 250 C. for about /2 to hour, and is then given a final cure at about C. for about 24 hours to drive off all of the benzoyl peroxide. The rubber is readily stripped from the faces of the plates. The pins are then removed. To facilitate this, the unit may be submerged in xylene to expand the silicone rubber of the capillary tubes to make the pins more easily removable. The unit is completed by vulcanizing the side wall portions and cover faces and inlets and outlets to the unit.

Polyvinyl chloride units are made similarly from cold suspensions of polyvinyl chloride. A metal mold of the type described is used, desirably made of metal so that it may be heated to facilitate deposition of the resin. The mold is desirably heated to about 180 C. Because the pins tend to dissipate heat rapidly when removed from the heat source, they may be maintained heated by making them part of an electrical current in which they afford-resistance sufiicient to heat the pins. The mold is dipped and redipped until the desired wall thickness has been built up and then the unit is cured. A silicone mold release compound may be used to facilitate withdrawal of the pins from the completed capillary tubes. The designations top, bottom, side, face, etc. used to describe portions of the fluid exchange device are relative only. Since the unit functions under pressure and its functioning is not dependent upon the effect of gravity, the device may generally be used in any position. Thus, it may be desired that the unit be disposed for use so that the face 15 would be the bottom, in which event face 16 would be the top and wall portions 11 and 12 would become side walls. -The liquid inlet tubes 23 and 24 and gas inlet tubes 26 and 27 may be located as desired so long as they communicate with the proper chambers. It is preferred that all inlets and outlets be disposed on a single wall of the unit, although it is obvious that it would function if this were not true. An oxygenator having the approximate dimensions of the exemplary unit described has a capacity of about one liter of blood per minute.

The oxygenator unit of this invention is a closed system which permits oxygenation of blood without the necessity of exposing the blood directly to a gas, since the permeable capillary membrane walls at all times intervene as a blood-gas barrier. Oxygen is introduced to the blood in exchange for carbon dioxide without the formation of gas bubbles in the blood. The fear of the possible formation and introduction of gas emboli into the blood stream is thus eliminated. In addition to its use in heartsurgery, the device may be used to oxygenate the blood from other organs or selected body zones for treatment by perfusion through an isolated segment of the circulatory system.

When the device of this invention is used to function as an artificial kidney, its structure is identical and its operation is substantially the sameas when used as an oxygenator. The chamber 25 surrounding the capillary tubes is then utilized as a liquid chamber through which solutions of proper ionic concentration are circulated and the inlet and discharge tubes 26 and 27 are used to introduce and discharge the liquid.

A circulation system incorporating the oxygenator of this invention will ordinarily be provided with means for introducing supplemental venous blood as described in Patent No. 2,854,002. Similarly, the coronary sinus suction device for returning cardiotomy loss to the patient through the oxygenator, as disclosed in that patent, may be utilized in connection with the oxygenator of this invention.

It is apparent that many modifications and variations of this invention as hereinbefore set forth may be made without departing from the spirit and scope thereof. The specific embodiments described are given by way of example only, and the invention is limited only by the terms of the appended claims.

I claim:

1. A fluid exchange device comprising a closed structure including a pair of generally parallel spaced apart face wall members each provided with a plurality of capillary openings, the capillary openings of one of said wall members being connected to the corresponding capillary openings of said other wall member by a plurality of thin-walled gas permeable capillary passages, the space between said wall members occupied by said capillary passages defining a fluid exchange chamber, a fiuid inlet to said chamber, and a fluid outlet from said chamber, a pair of liquid reservoirs each adjacent to the outer face of one of said wall members in communication with said capillary openings, a liquid inlet to one of said resen voirs, and a liquid discharge from the other of said reservoirs.

2. A liquid-gas exchange device comprising aclosed structure including a pair of generally parallel spaced apart perforated wall members each provided with a plurality of capillary openings, the capillary openings of one of said wall members being connected to the corresponding capillary openings of said other wall member by a plurality of thin-walled gas permeable capillary tubes, the space between said perforated wall members occupied by said capillary tubes defining a gas exchange chamher, a gas inlet to said chamber, and a gas outlet from said chamber, a pair of liquid reservoirs each adjacent the outer face of one of said wall members in communication with said capillary openings, a liquid inlet to one of said reservoirs, and a liquid discharge from the other of said reservoirs.

3. A device according to claim 2 further characterized in that said structure is generally rectangular in form having four walls, said pair of generally parallel spaced apart perforated wall members is supported within said walls spaced inwardly from the edges thereof and a cover sheet extending over said wall edges defines the outer wall of each of said liquid reservoirs.

4. A device accoring to claim 2 further characterized in that said structure is comprised of synthetic resinous material and said capillary tubes are formed integral with said face wall members.

5. A device according to claim 2 further characterized in that said capillary openings are from about 1 to 50 mils in diameter and said capillary tube wall thicknesses are from about /2 to 3 mils.

6. A blood oxygenator comprising a pair of generally parallel spaced-apart perforated wall members each provided with a plurality of fine capillary openings, the corresponding openings of said wall members being connected by thin-walled capillary tubes, the walls of said capillary tubes being comprised of synthetic resinous material permeable to the passage of carbon dioxide and oxygen, means enclosing the space between said wall members occupied by said capillary tubes and defining an oxygenating chamber, inlet means for introducing oxygen to said chamber and discharge means for discharging carbon dioxide therefrom, a shallow chamber adjacent the exposed face of each of said wall members in communication with the capillary openings therein and.means for introducing blood to one of said chambers and discharging blood from the other.

7. An oxygenator according to claim 6 further characterized in that said capillary tubes have diameters between about 1 and 50 mils and said wall thicknesses are between about /2 and 3 mils.

8. An oxygenator according to claim 6 further characterized in that said structure is generally rectangular in form having four walls, said pair of spaced-apart perforated wall members is supported within said four walls spaced inwardly from the edges thereof and a cover sheet extending over said wall edges defines the outer wall of eachof said blood chambers.

9. An oxygenator according to claim 6 further char acterized by being composed of synthetic resinous material and said capillary tubes are formed integral with said perforated wall members.

References Cited in the file of this patent UNITED STATES PATENTS Metz Apr. 7, 1959 Kollsman June 23, 1959 OTHER REFERENCES 

